The present invention relates to a fluid dosing device for a pressurized liquid with a chamber arranged in a housing, which is supplied with pressurized fluid by means of a liquid supply line and with a valve needle, which is guided through the chamber, the first end section of said valve needle being able to be lifted outside the chamber and the second end section thereof forming a valve which is connected to the housing, in conjunction with a valve seat provided on the housing.
Various sealing or leadthrough elements for fluid dosing devices are known in the prior art. In cases where pressurized fuel at a pressure of up to 300 bar for example and a working temperature of −40° C. to +150° C. is dosed, special requirements are set for mass-produced products. In particular exacting requirements must be complied with in respect of embrittlement, wear and reliability. The fatigue strength of the O-ring seals used up to now does not comply with the above requirements. Diaphragm seals such as for example metal beads, etc. can also be used in place of O-ring seals. When such diaphragms are used as the leadthrough element for a valve needle through a pressurized chamber however the requirements relating to high axial flexibility are not complied with when the compression strength is adequate.
The valve needle can also continue to be effected by means of a clearance fit of the needle in a cylindrical hole in the housing as in diesel injectors. A disadvantage of this is the unavoidable leakage along the needle leadthrough. The higher level of hydraulic loss also reduces the overall efficiency of the motor.